When construction work is undertaken the land is often disturbed and there may be a runoff or discharge which enters the storm water system or existing water courses, lakes or other water bodies. The concentration of various contaminants, including suspended solids needs to be controlled to prevent downstream detrimental effects. To do this governmental bodies place limits on the concentration of contaminants allowed in the discharge. To meet these standards those creating the discharge put in place measures to meet these concentration limits, but to ensure they are complied with testing needs to occur.
To measure the concentration of suspended solids in a laboratory the sample is often allowed to settle for a predetermined time to remove certain settleable material then filtered, normally through a glass filter with around 1.2 micrometer pore size to separate the suspended solids. The glass filter is weighed before filtering and then the retained material and filter dried to constant mass before reweighing and calculating the suspended solids. This method takes time and requires a skilled laboratory technician. For runoffs and discharges over a short timeframe (1 to 5 days) the cost and time taken make this method less than ideal, and it is very unlikely to be carried out on site.
Turbidity can be used as an indication of suspended solids but each discharge has specific characteristics, and a calibration curve relating the turbidity (optical obscuration) to the suspended solids loading in each specific discharge is required. Solids and other fine suspensions affect the turbidity though may not increase the suspended solids loading significantly.
There are turbidity meters available but these in general come with a high cost ($2000+) and require a separate calibration curve for each individual discharge. This may be justified for long term projects or wastewater/sewage plant discharges but for short term discharges it is neither cost effective nor practical. Further problems with the use of turbidity probes include recalibration if the discharge changes properties, keeping the probes clean and general maintenance of the equipment. Additionally the meters may be complicated to calibrate and use, and there use may be beyond the technical competence of some field staff.
Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.
It is the object of the present invention to provide a suspended solids test device that overcomes at least one of the deficiencies in existing measures or provides the consumer with a useful choice.